I have two 63s that are on my 104" PBN Nomad. For break-in I ran both well to the rich side for a bit over an hour each on a Balsa USA Stingray, both on wheels and on floats. Remembering that the engines were far from being fully broken in, were running rich and therefore the RPMs were low, on both engines the RPMs with APC 13x6 prop was 11,000. For the Nomad, due to clearance issues I will be using three-bladed props. After experimentation with the Stingray it appears that I will be using three-bladed 12x6 Master Airscrew props. These gave 12,500 RPM versus 9,900 for similar 12x8 props - again these were during break-in so there wasn't any intent to max. out the power.

Hope that this is helpful